1. Field of the Invention
The present invention relates generally to wireless communications. More specifically, the present invention relates to managing communication links to a wireless device during movement of the device between locations that are served by different network service providers.
2. Background of the Invention
Global system for mobile communication (GSM), one of the most widely used wireless access systems in today's market, employs so-called “cell” technology. Each cell contains a base transceiver station (BTS) to receive and broadcast radio frequency signals to the wireless communication device, such as a cell phone, personal digital assistant (PDA), or computer, all of which may be referred to as a mobile station (MS). In many geographic areas, particularly cities and metropolitan areas, more than one service provider of cellular communications may operate, each operating its own BTS, and base station controller (BSC), the latter often responsible for managing several BTS sites. Under normal conditions, a Mobile Switching Center (MSC) belonging to a customer's (subscriber's) operator is alerted to the location of the MS when the device is powered on. When a subscriber places a call within a region where her or his service provider operates (home region), the call is routed through the provider's network, which is sometimes referred to as a home public land mobile network, or HPLMN. The call is thus routed to the nearest BTS in the HPLMN, even if a BTS from another service provider is available. Thus, all the revenues associated with the call are realized by the subscriber's service provider.
However, there are many geographical areas where a typical service provider may not have a license to operate over the necessary frequency spectrum, or where it would be unduly expensive to deploy network resources, in light of the volume of calls generated. This situation might apply, for example, along major interstate freeways or in very rural areas, among others. In such areas, a service provider will often enter into a sharing agreement with another provider (partner) to receive access to coverage of the area for its customers. The shared network area (hereafter termed “partner region”) is designated as belonging to the partner and calls operating in the area are routed through the partner's network. In GSM, if a subscriber moves from an HPLMN into a partner region, GSM has the mechanisms in place to hand the call into the partner network.
As illustrated in FIG. 1, as MS 2, belonging to a subscriber to a home network, travels through home region 4, including cells 6 and 8, the call is directed to and from a BTS in cell 6, which is operated by the home network. During travel, MS 2 continues to monitor the frequencies of channels associated with nearby cells, to determine the signal strength of nearby BTS units (hereafter simply referred to as “cells”). This information is transmitted to the BSC (not shown), which instructs the MS to hand the call into a second cell 10, based on the cell signal strength, and other factors related to management of call traffic. As MS 2 continues to travel to the border of home region 4, the MS will monitor the signal strength of nearby cell 16. Because there are no nearby cells of the home network, a handoff will occur into cell 16 of partner region 14 if MS 2 continues to travel in the same direction. Also, if MS 2 is located in partner region 14 operated by the partner network, a new incoming call is automatically routed to the subscriber MS 2, through cell 16 of the partner network.
When MS 2 moves back to the border of a home region 20, there is no general mechanism to route the call back to the home network without creating artificial boundaries (i.e. MSC borders). In FIG. 1, home region 20 contains cells 22 and 24 belonging to the home and partner networks, respectively. Upon reaching a region between cells 16 and 20, MS 2 continues to send information regarding nearby cells to the BSC of the partner network, which instructs the MS to hand the call into a new cell. In routing the call through a nearby cell, the BSC knows to which network the cell belongs, but not to which network the MS/subscriber belongs. In the example shown in FIG. 1, the call is handed into cell 24, operated by the partner network, based on slightly higher signal strength than cell 22. Path 28 indicates the succession of cells handling the call from MS 2, as it travels along path 3. When MS 2 emerges into home region 20, rather than having the call routed through the home network cell 22, it remains routed through partner network cell 24. MS 2 then arrives at a location 26, where the call continues until termination. Although the signal strength of cell 22 may be more than sufficient to carry the call, the partner network continues to carry the call for its duration. This results in a loss of potential revenue to the home network operator for the duration of the call that takes place while the subscriber has entered the home region 20, but is routed through the partner network. Thus, the lack of means to direct a call handled by a partner back into a home network may result in significant lost revenue for an operator.
When viewed from the perspective of the partner network, the aforementioned scenario presents additional problems. Because of the inability to handover all calls associated with home network subscribers back to a cell in the home network, when any MS from the home network, whose call is being routed through the partner network, enters region 20, the resources of the partner network are unduly burdened with handling such calls that “should” be handed to the home network. This may result in inconvenience to, or lost revenue from, partner network subscribers who attempt to place calls in the region 20.
While the above example was directed towards illustrating problems existing with handover of voice communications between networks, similar problems can occur for data transmission to and from a mobile station. Using general packet radio service (GPRS), data is transmitted to or from a mobile device connected to a GSM service provider. When an MS belonging to a subscriber is in a partner region and approaches the border between a partner region and home region during a GPRS message, handoff to the home network is desired.
It is thus clear that there is a need to establish a system and method for communication between different mobile networks, where a call handled by a partner network can be handed back to the home network, as opposed to any other available network, when an MS enters a home region.